Since a low-noise imaging technology can be applied to various fields such as a biomedical field and a science field, the interest in low-noise imaging has been increasing in recent years. Although a circuit technology has progressed up to a noise level of around one noise electron, it is necessary to reduce the noise level further for the practical use of ultralow-noise imaging, which is called “photon counting”.
Conventionally, in a CCD image sensor in which a p-type semiconductor region is sandwiched between a n-type floating diffusion layer and a n-type reset-drain region, a method in which a pulse voltage is applied directly to the reset-drain region when resetting signal charges of the floating diffusion layer to cause punch-through to occur in a semiconductor region sandwiched between the floating diffusion layer and the reset-drain region to exhaust charges is known as recited in Patent Literature (PTL)1. According to the structure disclosed in PTL 1, since the reset-gate electrode of the earlier technology is not necessary and a parasitic capacitance between the reset-gate electrode and the floating diffusion layer disappears, it is expected to be able to reduce the capacitance of the floating diffusion layer and to improve the sensitivity.